Ternary chalcopyrite semiconductors are well known as promising materials for photovoltaic applications. The substitution of group IV atoms in sulfur and selenium copper gallium chalcopyrites GaCuX2, with X = S and Se, could have important implications either for photovoltaic or spintronic applications. To better understand these effects, we have made first-principles calculations on the doped chalcopyrites with group IV atoms, with different concentrations and geometries. Many of these materials have an intermediate band that modifies the optical properties of the host semiconductor. The sub-gap absorptions have also been determined using the absorption coefficients. (C) 2010 Elsevier B.V. All rights reserved.